Multiple Input Multiple Output (MIMO) transmission, in which a plurality of transmit antennas and a plurality of receive antennas are used for transmission, can increase the transmission rate without expanding the frequency bandwidth, and is thus used in Long Term Evolution (LTE), wireless Local Area Networks (LAN), and the like.
In recent years, MIMO transmission using a significantly increased number of antennas has received attention. Such MIMO transmission is referred to as Massive MIMO, Large Scale MIMO, Full Dimension MIMO, or the like. When the number of transmit antennas is notably greater than the number of receive antennas, a large difference is caused between the gain with respect to a desired signal and the gain with respect to an interference signal merely by using HH as a precoding matrix, where H is the channel matrix of MIMO. Thus, interference can be very easily reduced. Such Massive MIMO is disclosed in NPL 1.